đưa thừa số ra ngoài dấu căn của những biểu thức sau
a. \(\sqrt{27\left(9-4\sqrt{5}\right)}\)
b.\(\sqrt{a^4b^5}\)
c. \(\sqrt{a^3\left(1-a\right)^4}\) (a>1)
d. \(\sqrt{\dfrac{1}{a}-\dfrac{1}{a^2}}\left(a>1\right)\)
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Những câu hỏi liên quan
10 tháng 4 2021
a, Để A nhận giá trị dương thì \(A>0\)hay \(x-1>0\Leftrightarrow x>1\)
b, \(B=2\sqrt{2^2.5}-3\sqrt{3^2.5}+4\sqrt{4^2.5}\)
\(=4\sqrt{5}-9\sqrt{5}+16\sqrt{5}=\left(4-9+16\right)\sqrt{5}=11\sqrt{5}\)
( theo công thức \(A\sqrt{B}=\sqrt{A^2B}\))
c, Với \(a\ge0;a\ne1\)
\(C=\left(\frac{1-a\sqrt{a}}{1-\sqrt{a}}+\sqrt{a}\right)\left(\frac{1-\sqrt{a}}{1-a}\right)^2\)
\(=\left(\frac{\left(1-\sqrt{a}\right)\left(1+\sqrt{a}+a\right)}{1-\sqrt{a}}+\sqrt{a}\right)\left(\frac{1-\sqrt{a}}{\left(1-\sqrt{a}\right)\left(1+\sqrt{a}\right)}\right)^2\)
\(=\left(\sqrt{a}+1\right)^2.\frac{1}{\left(\sqrt{a}+1\right)^2}=1\)
2 tháng 7 2021
a) Ta có: \(A=\dfrac{a^2-1}{3}\cdot\sqrt{\dfrac{9}{\left(1-a\right)^2}}\)
\(=\dfrac{\left(a+1\right)\cdot\left(a-1\right)}{3}\cdot\dfrac{3}{\left|1-a\right|}\)
\(=\dfrac{\left(a+1\right)\left(a-1\right)}{1-a}\)
=-a-1
b) Ta có: \(B=\sqrt{\left(3a-5\right)^2}-2a+4\)
\(=\left|3a-5\right|-2a+4\)
\(=5-3a-2a+4\)
=9-5a
c) Ta có: \(C=4a-3-\sqrt{\left(2a-1\right)^2}\)
\(=4a-3-\left|2a-1\right|\)
\(=4a-3-2a+1\)
\(=2a-2\)
d) Ta có: \(D=\dfrac{a-2}{4}\cdot\sqrt{\dfrac{16a^4}{\left(a-2\right)^2}}\)
\(=\dfrac{a-2}{4}\cdot\dfrac{4a^2}{\left|a-2\right|}\)
\(=\dfrac{a^2\left(a-2\right)}{-\left(a-2\right)}\)
\(=-a^2\)
DH
6 tháng 7 2017
a, \(\sqrt{5\left(1-\sqrt{2}\right)^2}=\sqrt{5}.\sqrt{\left(1-\sqrt{2}\right)^2}\)
\(=\sqrt{5}.\left(1-\sqrt{2}\right)=\sqrt{5}-\sqrt{5}.\sqrt{2}=\sqrt{5}-\sqrt{10}\)
b, \(\sqrt{27\left(2-\sqrt{5}\right)^2}=\sqrt{27}.\sqrt{\left(2-\sqrt{5}\right)^2}\)
\(=\sqrt{27}.\left(2-\sqrt{5}\right)=2\sqrt{27}-\sqrt{135}\)
c, \(\sqrt{\dfrac{2}{\left(3-\sqrt{10}\right)^2}}=\dfrac{\sqrt{2}}{\sqrt{\left(3-\sqrt{10}\right)^2}}\)
\(=\dfrac{\sqrt{2}}{3-\sqrt{10}}\)
d, \(\sqrt{\dfrac{5\left(1-\sqrt{3}\right)^2}{4}}=\dfrac{\sqrt{5\left(1-\sqrt{3}\right)^2}}{\sqrt{4}}\)
\(=\dfrac{\sqrt{5}.\left(1-\sqrt{3}\right)}{2}=\dfrac{\sqrt{5}-\sqrt{15}}{2}\)
Chúc bạn học tốt!!!
6 tháng 7 2017
a) \(\sqrt{5\left(1-\sqrt{2}\right)^2}\)
= \(\sqrt{5}.\sqrt{\left(1-\sqrt{2}\right)^2}\)
= \(\sqrt{5}.\left(\sqrt{2}-1\right)\)
= \(\sqrt{10}-\sqrt{5}\)
b) \(\sqrt{27\left(2-\sqrt{5}\right)^2}\)
= \(\sqrt{27}.\sqrt{\left(2-\sqrt{5}\right)^2}\)
= \(\sqrt{27}.\left(\sqrt{5}-2\right)\)
= \(\sqrt{135}-2\sqrt{27}\)
c) \(\sqrt{\dfrac{2}{\left(3-\sqrt{10}\right)^2}}\)
= \(\dfrac{\sqrt{2}}{\sqrt{\left(3-\sqrt{10}\right)^2}}\)
= \(\dfrac{\sqrt{2}}{\sqrt{10}-3}\)
d) \(\sqrt{\dfrac{5\left(1-\sqrt{3}\right)^2}{4}}\)
= \(\dfrac{\sqrt{5}.\sqrt{\left(1-\sqrt{3}\right)^2}}{\sqrt{4}}\)
= \(\dfrac{\sqrt{5}.\left(\sqrt{3}-1\right)}{2}\)
= \(\dfrac{\sqrt{15}-\sqrt{5}}{2}\)
15 tháng 8 2021
\(\sqrt{18b^3\cdot\left(1-2a\right)^2}\)
\(=3\sqrt{2}\cdot b\sqrt{b}\cdot\left|1-2a\right|\)
\(=3\sqrt{2}\left(2a-1\right)\cdot b\sqrt{b}\)
NV
Nguyễn Việt Lâm
Giáo viên
11 tháng 1
\(E=a^{12-4}.b^{3-7}=\dfrac{a^8}{b^4}\)
\(E=a^{4-6}.b^{3.4}=\dfrac{b^{12}}{a^2}\)
\(F=\dfrac{a^{\left(\sqrt{3}-1\right)\left(\sqrt{3}+1\right)}}{a^{\left(\sqrt{5}-3\right)+\left(4-\sqrt{5}\right)}}=\dfrac{a^2}{a^1}=a\)
10 tháng 7 2021
Sửa đề: \(Q=\left(\dfrac{1}{\sqrt{a}-1}-\dfrac{1}{\sqrt{a}}\right):\left(\dfrac{\sqrt{a}+1}{\sqrt{a}-2}-\dfrac{\sqrt{a}-1}{\sqrt{a}+2}\right)\)
a) ĐKXĐ: \(\left\{{}\begin{matrix}a\ge0\\a\notin\left\{1;4\right\}\end{matrix}\right.\)
Ta có: \(Q=\left(\dfrac{1}{\sqrt{a}-1}-\dfrac{1}{\sqrt{a}}\right):\left(\dfrac{\sqrt{a}+1}{\sqrt{a}-2}-\dfrac{\sqrt{a}-1}{\sqrt{a}+2}\right)\)
\(=\dfrac{\sqrt{a}-\sqrt{a}+1}{\sqrt{a}\left(\sqrt{a}-1\right)}:\dfrac{a+3\sqrt{a}+2-a+3\sqrt{a}-2}{\left(\sqrt{a}-2\right)\left(\sqrt{a}+2\right)}\)
\(=\dfrac{1}{\sqrt{a}\left(\sqrt{a}-1\right)}\cdot\dfrac{\left(\sqrt{a}-2\right)\left(\sqrt{a}+2\right)}{6\sqrt{a}}\)
\(=\dfrac{a-4}{6a\left(\sqrt{a}-1\right)}\)
c) Thay \(a=9-4\sqrt{5}\) vào Q, ta được:
\(Q=\dfrac{5-4\sqrt{5}}{6\left(9-4\sqrt{5}\right)\left(\sqrt{5}-3\right)}\)
\(=\dfrac{5-4\sqrt{5}}{6\left(9\sqrt{5}-27-20+12\sqrt{5}\right)}\)
\(=\dfrac{5-4\sqrt{5}}{6\left(21\sqrt{5}-47\right)}\)
\(=\dfrac{\left(5-4\sqrt{5}\right)\left(21\sqrt{5}+47\right)}{-24}\)
\(=\dfrac{105\sqrt{5}+235-420-188\sqrt{5}}{-24}\)
\(=\dfrac{-83\sqrt{5}-185}{-24}=\dfrac{83\sqrt{5}+185}{24}\)
CP
16 tháng 7 2021
a) \(A=\left(1-\dfrac{\sqrt{3}-1}{2}\right):\left(\dfrac{\sqrt{3}-1}{2}+2\right)\)
\(=\left(\dfrac{2}{2}-\dfrac{\sqrt{3}-1}{2}\right):\left(\dfrac{\sqrt{3}-1}{2}+\dfrac{4}{2}\right)\)
\(=\dfrac{2-\left(\sqrt{3}-1\right)}{2}:\dfrac{\left(\sqrt{3}-1\right)+4}{2}\)
\(=\dfrac{3-\sqrt{3}}{2}.\dfrac{2}{\sqrt{3}+3}\)
\(=\dfrac{\sqrt{3}\left(\sqrt{3}-1\right)}{\sqrt{3}\left(1+\sqrt{3}\right)}\)
\(=\dfrac{\left(\sqrt{3}-1\right)\left(\sqrt{3}-1\right)}{\left(\sqrt{3}+1\right)\left(\sqrt{3}-1\right)}\)
\(=\dfrac{\left(\sqrt{3}-1\right)^2}{2}\)
Vì \(\left\{{}\begin{matrix}\left(\sqrt{3}-1\right)^2>0\\2>0\end{matrix}\right.\) \(\Rightarrow\dfrac{\left(\sqrt{3}-1\right)^2}{2}>0\) hay A>0
=> A có căn bậc 2
Vậy......
b)\(B=\left(\dfrac{\sqrt{6}-\sqrt{2}}{1-\sqrt{3}}-\dfrac{5}{\sqrt{5}}\right):\dfrac{1}{\sqrt{5}-\sqrt{2}}\)
\(=\left(\dfrac{\sqrt{2}\left(\sqrt{3}-1\right)\left(1+\sqrt{3}\right)}{\left(1-\sqrt{3}\right)\left(1+\sqrt{3}\right)}-\sqrt{5}\right):\dfrac{\sqrt{5}+\sqrt{2}}{\left(\sqrt{5}-\sqrt{2}\right)\left(\sqrt{5}+\sqrt{2}\right)}\)
\(=\left(\dfrac{\sqrt{2}\left(3-1\right)}{1-3}-\sqrt{5}\right).\dfrac{5-2}{\sqrt{5}+\sqrt{2}}\)
\(=\left(-\sqrt{2}-\sqrt{5}\right).\dfrac{3}{\sqrt{5}+\sqrt{2}}\)
\(=-\left(\sqrt{2}+\sqrt{5}\right).\dfrac{3}{\sqrt{5}+\sqrt{2}}\)
\(=-3\)
Vì -3 < 0 hay B < 0
=> B không có căn bậc 2
Vậy.....
a) \(\sqrt{27\left(9-4\sqrt{5}\right)}=3\sqrt{3\left(\sqrt{5}-2\right)^2}=3\sqrt{3}\left(\sqrt{5}-2\right)=3\sqrt{15}-6\sqrt{3}\)
b) \(\sqrt{a^4b^5}=a^2b^2\sqrt{b}\)
c) \(\sqrt{a^3\left(1-a\right)^4}=a\left(1-a\right)^2\sqrt{a}\)
d) không biết